The present invention relates to a structure of a wiring board (or a circuit board), a producing method thereof, a semiconductor device, a producing method thereof, which are used in common electronic apparatuses each comprising a board(s) carrying an LSI(s), and an electronic apparatus, especially the same as above and a semiconductor device package structure which are suitable for such electronic apparatuses which are required to meet the compatibility between high reliability and a lower manufacturing cost.
Such a conventional wiring board can be seen in JP-A-62-263661.
According to the prior art, the multi-layered metal structure of which layers are interconnected with one another on a board and which comprises a bond layer consisting of an element selected from the group of Ti, Ba, Cr and Ta, which is deposited on the board, a stress relaxation layer consisting of an element selected from the group of Cu, Fe, Al, Ag, Ni and Au, which is deposited on the bond layer, a barrier layer consisting of Ti or Zr and a wettable surface layer.
In the case where a solder is brought into direct contact with a wiring layer in order to connect a wiring board with an outer circuit, there will occur a phenomenon that composition elements of the solder and the wiring layer migrate each other between them during soldering or by a change with the passage of time after soldering resulting in loss of component elements of a wiring material (so called xe2x80x9csolder damagexe2x80x9d). Since an alloy layer is produced from the elements derived from the solder and the wiring layer under the phenomenon, there will arise a problem of harmful effects that the bonding part becomes brittle and of high electric resistance. If the xe2x80x9csolder damagexe2x80x9d further develops, the solder reaches the bottom face of the wiring material to deteriorate adhesion between the wiring material and an under layer so that the bonding part is delaminated from the under layer resulting in a defective product.
Therefore, in order to prevent occurrence of the above defect at the bending portion by soldering, the following two countermeasures have been usually adopted.
One method thereof is to prevent the solder from reaching the bottom face of the wiring material during the producing method and operation of the apparatus by making the wiring material thick.
Another method is to protect the wiring from the solder by providing a protective coating onto the wiring, which has high resistance against the solder damage, and by stopping the migration due to the solder within the protective coating.
The former method of making the wiring material thick does not solve the problem of strength reduction due to the formation of the alloy layer produced at the bonding part and causes some technical difficulties in other processes including a process of forming an insulation layer and another forming process because of an increase of the thickness of the wiring material.
In case of forming the protective coating layer with high resistance against the solder, namely the solder diffusion barrier layer called the UBM (Under Bump Material) or BLM (Ball Limiting Metallurgy) according to the latter method, a metal layer which is not usually used for wiring materials, for example, Ni, Nixe2x80x94Cr, Nixe2x80x94Cu, Pt, etc. must be additionally formed and processed so that the process steps increase and a higher level technology will be required.
On the other hand, because of demands for higher performance and more multi-function of electronic apparatuses, the total length of the wiring to be accommodated in the wiring board used for them is rapidly increasing so that the wiring becomes further finer and a further advanced multi-layer is required. Furthermore, in view of transfer quality of signals in a wiring board, requirements for the form of wiring and the positional accuracy of wiring, etc. become more strict and severer so that, for keeping the function at connecting portions with outside as stated in the above, it becomes difficult to change specifications for wiring. Therefore, in case of advanced electronic apparatuses, specifications for wiring are determined on the basis of electrical characteristics so that a structure, in which connecting electrodes with a material having higher resistance against the solder damage are provided to another layer, is becoming the main current. But, such a structure has a problem that process steps increase and a higher level technology is required leading to a remarkably higher production cost.
Further, with regard to the fine wiring on wiring boards hereafter, it will be necessary to apply soldering to a wiring board with solder-connecting electrodes each having a small surface area, which is called xe2x80x9cmicro-solderingxe2x80x9d. Especially, for a metal composition and a thickness of the UBM and forming thereof, a much higher level technology will be required in the future.
An object of the invention is to provide a wiring board and a semiconductor device having a high density and high reliability in solder-connecting.
Another object of the invention is to provide methods of producing a wiring board and a semiconductor device in which the wiring board and the semiconductor device each having a high density and high reliability in solder-connecting can be produced at a low cost.
A still further object of the invention is to provide an electronic apparatus and a semiconductor device package structure which have a wiring board and a semiconductor device each having a high density and high reliability in solder-connecting and being capable of a low cost production.
Under the objects, according to the present invention, there is provided a wiring board which comprises:
an insulation layer formed on the wiring board; and
a wiring consisting of a Cu layer and a Cr or Ti layer which is arranged between the Cu layer and the insulation layer under the Cu layer in order to closely connect the Cu layer with the insulation layer, wherein
a solder for the outer connection is provided on the Cu layer and brought to diffuse into the Cu layer to produce an alloy, and brought to reach the Cr or Ti layer thereby connecting the solder to the Cr or Ti layer.
According to the present invention, there is provided also a wiring board which comprises:
a board having an electrode and being coated with an insulation layer with a hole for exposing the electrode;
a wiring consisting of a Cr or Ti layer, which is connected to the electrode and closely contacts with the insulation layer, and a Cu layer which is closely contacts with the Cr or Ti layer;
a protective film which covers the wiring and is provided with another hole for soldering; and
a solder for the outer connection which is mounted in the both holes and brought to diffuse into the Cu layer to produce an alloy, and which reaches the Cr or Ti layer thereby connecting the solder to the Cr or Ti layer.
The followings are preferable embodiments of the invention:
The solder for the outer connection used in the wiring board may comprise Sn.
The Cu layer in the wiring board may have a thickness of from about 0.1 xcexcm to about 10 xcexcm.
In the wiring board, the Cr layer may be provided between the Cu layer and the insulation layer.
The insulation layer in the wiring board may comprise an organic resin layer.
The solder for the outer connection used in the wiring board may be directly connected to the wiring layer which is connected to the electrode on the wiring board.
An Au layer, an Nixe2x80x94Au layer or a rust prevention layer such as preflux may be provided between the solder for the outer connection and the Cu layer in the wiring board in order to improve wettability of the solder.
According to the invention, there is provided also an electronic apparatus in which a solder for the outer connection in a wiring board is connected to electronic components.
According to the invention, there is provided also a method of producing a wiring board, which comprises the following steps:
a step of forming an insulation layer on a wiring board;
a step of forming a wiring, in which a Cr or Ti layer and a Cu layer are laminated on the insulation layer formed in the prior step; and
a reflow bonding step, in which a solder for the outer connection is provided on the Cu layer and brought to diffuse into the Cu layer to produce an alloy, which reaches the Cr or Ti layer thereby connecting the solder to the Cr or Ti layer.
According to the invention, there is provided also a method of producing a wiring board, which comprises the following steps:
a step of forming an insulation film, which comprises coating a wiring board having an electrode by the insulation film and forming a hole in the insulation film in order to expose the electrode;
a step of forming a wiring, in which a Cr or Ti layer is connected to the electrode and brought into close contact with the insulation film, and a Cu layer is closely laminated on the Cr or Ti layer;
a step of forming a protective film, which comprises coating the wiring, being formed in the prior step, with the protective film and forming another hole in the protective film for soldering; and
a reflow bonding step, in which a solder for the outer connection is provided within the hole of the protective film and brought to diffuse into the Cu layer in the wiring to produce an alloy, which reaches the Cr or Ti layer thereby connecting the solder to the Cr or Ti layer.
According to the invention, there is provided also a semiconductor device which comprises:
a semiconductor board having an electrode and being coated with an insulation layer being formed with a hole in order to expose the electrode;
a wiring consisting of a Cr or Ti layer which is close contact with the insulation layer and of a Cu layer which is closely laminated on the Cr or Ti layer;
a protective film covering the wiring and being formed with a hole for soldering; and
a solder for the outer connection which is provided within the hole of the protective film and brought to diffuse into the Cu layer in the wiring to produce an alloy which reaches the Cr or Ti layer thereby connecting the solder to the Cr or Ti layer.
In the wiring of the semiconductor device, preferably the Cr layer may be provided between the Cu layer and the protective film.
In the semiconductor device, the insulation layer may comprise an organic resin layer.
According to the invention, there is provided a semiconductor device package structure in which a solder for the outer connection is connected to an electronic component such as a package board.
As is described in the above, according to the present invention, since the UBM is not needed to form, manufacturers can be released from an additional process of forming the UBM and technical difficulty. Further, since the wiring can be determined only by an electrically required thickness thereof regardless connecting portions, it is possible to improve electrical characteristics of the wiring. A further advantage is a realized cost reduction because of less steps of the whole producing method.